Throughout industry there is often the requirement to efficiently and economically disperse liquids on the surfaces of particles which should not undergo mechanical damage or abrasion. Moreover, many of these particles are collectively crowded together to form a composite product. The integral strength success of the composite product, where for example the liquids are binders, is based on the uniform or near uniform dispersement of the liquid throughout all the surface areas of the particles.
These factors are especially true when wood products are being manufactured. However, present methods and available apparatus do not completely fulfill all of the currently desired economic, quality and efficiency objectives.
In this regard in respect to the wood wafer board industry dispersement of resin binders is now undertaken in blenders, wherein finely pulverized dry resin is applied to wood wafers via tumbling within an inclined rotating drum. The dry resin, so pulverized, is obtained at a higher cost than liquid resins. In the particle board industry wood chips are sprayed with liquid resins while the wood chips undergo intense agitation. The liquid resin is sprayed into the turbulent mass of wood chips via air atomization or via fluid pressure nozzles. These wood chip blenders have nozzles which produce droplets in an unwanted wide dispersion of droplet sizes. Their air driven atomization sprays tend to carry the finest droplets of resin out in air venting streams, thus creating a nuisance while wasting resin. Moreover, in these wood chip blenders, the intense agitation produces heat and creates more fine material from the particles, that in turn, tends to absorb a disproportionate fraction of the consumed resin. In addition, resin-particle agglomerates tend to build up on the walls and paddles of these blenders requiring frequent costly cleaning maintenance.
In respect to information presented in U.S. patents, W. Wirz in his U.S Pat. No. 4,193,700 of Mar. 18, 1980 disclosed a short length drum, with internal vanes of lifters, rotated to yield an intermittent cascade of particles, while a spray nozzle dispersed a binder in an axial direction, from the feed end of the drum into the particle cascade. Also K. Engels in his U.S. Pat. No. 4,188,130 of Feb. 12, 1980 illustrated and described a drum with internal lifters to rotary lift particles for their subsequent cascading, while at the feed end of the drum, nozzles axially sprayed liquid resin toward the particles. Although Messrs. Wirz and Engels' apparatus comparatively gently handled the particles, the reliance on axially directed sprays required a high droplet concentration of liquid resin to achieve a reasonable output rate of treated particles. Such high concentration of resin droplets tends to yield a wide range in droplet size and reduces the opportunity for uniform coverage of the particles. Moreover, because one third to two thirds of their interior drum surfaces and lifters are also exposed to the spray of resin, there is the wasteful accumulation of resin on these exposed interior surfaces, also incurring cleaning maintenance costs.
Improved dispersement of liquid resins is also needed in the emerging structural board manufacturing processes, wherein carefully sliced wood wafers and flakes are used. To attain maximum panel strengths of these structural boards the sliced wood wafers and flakes should remain undamaged in blending operations and thereafter they should be aligned, as described by H. D. Turner in an article entitled "Structural Flakeboard Stiffness--Relation to Deflection Criteria and Economic Performance", as published in Forest Products Journal Volume 27, Number 12, December 1977.
In respect to all such related uses of resins, the distribution of the resins must be very efficient. Resin, at five percent of the dry wood weight, has a resin cost which is about one half of the wood cost. Usually the resin cost is the second largest cost element in wood board manufacturing.
Therefore, gentle handling of flakes and maximum efficiency of the resin distribution with minimum losses of resin are both important objectives in operating wood board processes, and especially in operating structural board processes wherein the wood wafers and wood flakes are aligned.